Frisian Flag is an annually occurring NATO exercise that is hosted by the Leeuwarden Air Base in Holland. It contains a mix of planes from different countries and the 2015 exercise contained Dutch F-16, USAF (Air National Guard) F-15, Finnish and Spanish F-18, German Eurofighters and a Dutch C-130.

As this is an exercise, what you get are take-offs and landings, with a morning and an afternoon sortie and each launch/landing of all aircraft takes about 45 minutes. Leeuwarden Air Base is a pretty good place, when it comes to spotting possibilities, with the "Spotter's Hill" as the most popular place. It's recommended that you get there early, if you want a good spot. Bringing a ladder is also recommended as will help you get better pictures. A more detailed description of the spotting/photo opportunities can be found here: http://www.scramble.nl/airfield-guide/leeuwarden

Please note that the event is a bit weather-pending and if the winds blow in the "wrong" direction", you end up seeing all take-offs and landing in the same direction.

What you want, is westerly winds, so that they start from runway 23 which give you some nice photo opportunities from Spotters hill.